An all-pass phase-shift network is an electrical circuit that ideally passes all frequencies of operation equally in magnitude, but changes the phase relationship over a range of frequencies. The phase-relationship variation is accomplished by the fact that the propagation delay of the phase-shift circuit varies with frequency. In other words, a phase-shift network provides phase shift or phase delay without appreciably altering the magnitude characteristic of the electrical signal passing through it. Hence, a phase-shift network may be useful in various electronic applications.
Phase-shift networks having frequency cutoffs outside the bandwidth of interest are useful in high-frequency coupling circuits. Such networks may be employed in various forms of hybrid couplers or other directional coupling circuits. These networks are discussed in our prior U.S. application Ser. No. 13/083,180 filed on Apr. 8, 2011.